1. Field of the Invention
The present invention relates to an ink, an ink set, an ink cartridge, a recording unit, a color-image recording apparatus, an image recording process, a color-image forming process, and a method for improving the density of an ink-Jet recorded image.
2. Related Background Art
Inks using carbon black which is a black colorant capable of providing prints high in optical density and excellent in fastness properties and the like have heretofore been proposed as black inks for writing utensils (fountain pens, felt-tip pens, ball-point pens, etc.) and black inks for ink-jet.
In recent years, detailed researches and developments have been made from various approaches such as composition and physical properties of inks so that good recording can be made even on plain paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous slip paper which are commonly used in offices. For example, Japanese Patent Application Laid-Open Nos. 63-152681 and 64-6074 disclose water-based pigment inks comprising carbon black and a dispersing agent. Japanese Patent Application Laid-Open No. 8-3498 has offered a technical problem that when an ink comprising carbon black together with a dispersing agent is used as an ink for ink-jet printer, ejection becomes unstable, or sufficient optical density is not achieved, and discloses a water-based pigment ink using a self-dispersing carbon black, but using no dispersing agent, as an ink capable of solving such a problem.
When printing is conducted on paper having high permeability, such as plain paper, with the conventional water-based inks, sharpness of characters printed may be impaired, or image density may be deteriorated to impair image quality in some cases In order to solve such a problem, it is considered to improve the coloring ability of inks by causing the inks not to penetrate into a recording medium as much as possible. In this case, however, another problem arises: the inks remain on the recording medium without penetrating into the recording medium, and so-called xe2x80x9cbleedingxe2x80x9d between different colors occurs at boundaries between them when a color image is formed.
It is therefore an object of the present invention to solve the above-described problems involved in the prior art and provide an ink, an ink set, an ink cartridge, a recording unit, a color-image recording apparatus, an image recording process and a color-image forming process which can prevent influence on image quality by the kinds of recording media, stably provide images excellent in image quality, effectively inhibit the occurrence of bleeding upon the formation of-color images and are excellent in long-term shelf stability in ink.
Another object of the present invention is to provide a water-based ink for ink- et, which can provide images extremely high in optical density, is low in dependence of the image density on recording media, has excellent stability and is hard to cause bleeding with another color ink on a recording medium when it is used in color recording.
A further object of the present invention is to provide a method for further improving the density of an image obtained by an ink-jet recording method using an ink containing a self-dispersing carbon black.
The above objects can be achieved by the present invention described below.
According to an embodiment of the present invention, there is thus provided an ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (xcexcmol/m2) on its surface.
According to another embodiment of the present invention, there is also provided an ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 0.45 (mmol/g) on its surface, the ink undergoing no substantial change in viscosity even when it is stored for one month in an environment of 60xc2x0 C.
According to an embodiment of the present invention, there is further provided an ink set comprising in combination a water-based color ink comprising at least one coloring material selected from among coloring materials for cyan, magenta, yellow, red, green and blue, and the above-described ink according to the present invention.
According to an embodiment of the present invention, there is still further provided an ink cartridge comprising an ink tank which contains the above-described ink according to the present invention
According to an embodiment of the present invention, there is yet still further provided a recording unit comprising an ink container portion containing an ink-jet ink and a head portion for ejecting the ink, the ink-jet ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (xcexcmol/m2) on its surface.
According to an embodiment of the present invention, there is yet still further provided an image recording apparatus comprising an ink-jet ink and a recording head for ejecting the ink, the ink-jet ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (xcexcmol/m2) on its surface.
According to another embodiment of the present invention, there is yet still further provided a color-image recording apparatus comprising an ink container portion containing an ink-jet ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, Ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (xcexcmol/m2) on its surface, another ink container portion containing a water-based, ink-set color ink comprising at least one coloring material selected from among coloring materials for cyan, magenta, yellow, red, green and blue, and recording head portions for respectively ejecting the inks contained in the respective ink container portions.
According to an embodiment of the present invention, there is still further provided an image recording process comprising the step of ejecting an ink-jet ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (xcexcmol/m2) on its surface toward the surface of a recording medium to apply the ink to the surface thereof, thereby recording an image.
According to an embodiment of the present invention, there is still further provided a process for forming a color image comprising the steps of ejecting a first water-based, ink-jet ink comprising at least one coloring material selected from among coloring materials for cyan, magenta, yellow, red, green and blue toward the surface of a recording medium to apply the ink to the surface thereof; and ejecting a second ink-jet ink comprising at least one salt selected from the group consisting of (M1)2SO4, CH3COO(M1), Ph-COO(M1), (M1)NO3, (M1)Cl, (M1)Br, (M1)I, (M1)2SO3 and (M1)2CO3, wherein M1 represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group, and a self-dispersing anionic carbon black having a functional-group density of at least 1.8 (xcexcmol/m2) on its surface toward the surface of the recording medium to apply the second ink to the surface thereof.
When such constitution is adopted, the dispersibility of the self-dispersing carbon black in the ink can be still more stabilized by making the functional-group density on its surface a level as high as at least 1.8 (xcexcmol/m2) or at least 0.45 (mmol/g). On the other hand, the salt is contained in the ink, whereby solid-liquid separation in the ink after the ink is applied to the recording medium can be quickly caused, and so both stability of self-dispersing carbon black in the ink and the image density by the ink, which have heretofore been considered to be difficult to be reconciled can be reconciled at a high level. By making solid-liquid separation faster, the bleeding with another ink on the recording medium when such an ink is used in recording of color images can be effectively inhibited.
According to another embodiment of the present invention, there is yet still further provided a water-soluble ink-jet ink comprising a self-dispersing carbon black having an average particle diameter of at least 90 nm and stably dispersed in an aqueous medium, and a salt, wherein the density of an image obtained by the ink is lowered when the salt is not contained.
According to an embodiment of the present invention, there is yet still further provided a method for improving the image density of an ink-jet recorded image formed with an ink comprising a self-dispersing carbon black having an average particle diameter of at least 90 nm and stably dispersed in an aqueous medium, the method comprising causing a salt to be contained as an agent for inhibiting penetration of the self-dispersing carbon black into the interior of a recording medium in the inks
By adopting such an embodiment, an image having such a high density that cannot be achieved by the sole use of self-dispersing carbon black having a great particle diameter can be obtained.